iTunes 4 lets you see how many users are connected to your shared stream, but not what they're listening to. Terminal to the rescue! Use lsof to figure out who's listening to what:
% lsof | grep mp3 % lsof | grep m4aEtcetera, etcetera. This only works if you use filename suffixes, though. Or, if you'd just like to see everything at once, and all your music is in a central music folder, for example, "Music", do this:
% lsof | grep MusicWoot! Perhaps this will make its way into iTunes as an update at some point.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030430141817856